A work machine such as a wheel loader generally travels by transmitting the power of an engine to wheels through a torque converter and a transmission. The transmission has a plurality of gears and changes the gear ratio by shifting the gears. Transmission gear shifting is achieved by a gear shifting control system. There are two gear shifting modes: a manual gear shifting mode and an automatic gear shifting mode. The automatic gear shifting mode generally includes a plurality of modes that differ in gear shifting conditions such as a vehicle velocity at a gear shifting point.
A typical work machine having a gear shifting control system described above is disclosed, for instance, in Japanese Patent JP-A-7-208594. The known technology disclosed in Japanese Patent JP-A-7-208594 provides increased work efficiency by offering four modes (free-traveling mode and work modes 1 to 3) and allowing an operator to select an appropriate mode with a switch in accordance with the road surface condition and soil property of a work site.    Patent Document 1: Japanese Patent JP-A-7-208594